The present invention relates to a torque converter into which a driving power is transferred from a driving power source such as an engine, and specifically to technologies for providing a flattened torque converter while enhancing operating characteristics of the torque converter.
European Patent Application No. EP 1 099 879 (hereinafter is referred to as xe2x80x9cEP1099879xe2x80x9d and corresponding to Japanese Patent Provisional Publication No. 2001-141026) discloses a flattened torque converter that a ratio 2L/H of the sum 2L of an axial length of a pump impeller (a driving torus) and an axial length of a turbine runner (a driven torus) to the difference H (=Rxe2x88x92r) between a torus outside radius R (that is, an outside radius of a working-fluid passage defined in the driving torus and driven torus) and a torus inside radius r (that is, an inside radius of a working-fluid passage defined in a stator disposed between the pump impeller and turbine runner) is set at a comparatively small value so as to reduce the axial size to radial size of the torque converter. More concretely, in the flattened torque converter disclosed in EP1099879, the ratio 2L/H of the sum 2L of the driving-torus axial length and the driven-torus axial length to the difference H (=Rxe2x88x92r) between the torus outside radius R and the torus inside radius r is set to satisfy an inequality 0.55 less than 2L/H less than 0.75. Additionally, a ratio r/R of the torus inside radius r to the torus outside radius R is set to satisfy an inequality 0.35 less than r/R less than 0.40. Furthermore, in the flattened torque converter disclosed in EP1099879, on the assumption that a point O on the central position of the working-fluid passage defined in the driving torus and driven torus and on a rotating shaft (a turbine shaft) is taken as origin, a line OX directed in the axial direction is taken as X-axis, and a line OY directed in the direction perpendicular to the axial direction is taken as Y-axis, the shape and dimensions of the working-fluid passage in the turbine (driven torus) are set or determined as follows. That is, the shape and dimensions of the working-fluid passage in the turbine (driven torus) are set or determined, so that a tangent point P between a 45xc2x0-inclined straight line C with respect to the X-axis and a curved line D contouring the outside curved surface of the working-fluid passage of the turbine (driven torus) is located within a specified area defined between first and second straight lines A and B. The first straight line A is represented by a predetermined linear equation Y=(R/L)xc2x7X+(6/4)xc2x7R, where R is the torus outside radius, L is the driving-torus axial length (or the driven-torus axial length), whereas the second straight line B is represented by a predetermined linear equation Y=(R/L)xc2x7X+(7/4)xc2x7R. In other words, EP1099879 merely teaches the reduction in a radius of curvature of the outer peripheral curved surface defining the outer peripheral working-fluid passage of the turbine (driven torus) so as to smooth internal working-fluid flow along the turbine outer peripheral curved surface of the reduced radius of curvature. This is advantageous with respect to reduced loss of fluid (suppressed turbulent flow) at the turbine inflow section, thus enhancing the torque absorbing capacity and power transmission capacity.
However, EP1099879 merely teaches the reduction in a radius of curvature of the outer peripheral curved surface defining the outer peripheral working-fluid passage of the turbine for the purpose of smooth internal working-fluid flow along the turbine outer peripheral curved surface by positioning the tangent point P between the 45xc2x0-inclined straight line C and the curved line D contouring the outside curved surface of the working-fluid passage of the turbine within the specified area defined between the first straight line A defined by Y=(R/L)xc2x7X+(6/4)xc2x7R) and the second straight line B defined by Y=(R/L)xc2x7X+(7/4)xc2x7R). EP1099879 fails to exactly define the interrelation between a radius of curvature of the outer peripheral curved surface defining the outer peripheral working-fluid passage of the turbine and a radius of curvature of the inner peripheral curved surface defining the inner peripheral working-fluid passage of the turbine. Additionally, EP1099879 teaches that in designing a working-fluid passage of the torque converter, usually, every cross section of the working-fluid passage is dimensioned to have the same cross-sectional area and thus dimensions of the inner peripheral curved surface defining the inner peripheral working-fluid passage of the turbine are determined by setting dimensions of the outer peripheral curved surface defining the outer peripheral working-fluid passage of the turbine. In the working-fluid passage design as disclosed in EP1099879, assuming that the previously-discussed ratio 2L/H is reduced in order to more greatly flatten the torque converter in the axial direction, there is a tendency for a radius of curvature of the inner peripheral curved surface defining the inner peripheral working-fluid passage of the turbine (or the pump impeller) to be reduced. This results in an increase in curvature loss (energy loss due to curvature) of working fluid at the outflow section of the pump impeller and at the inflow section of the turbine runner, thereby lowering a torque converter efficiency. In this case, the working fluid (working oil) tends to be broken away the turbine blade at the inner peripheral edged portion of the turbine blade or at the outer peripheral edged portion of the turbine core. As a result of this, an actual fluid-flow passage area tends to decrease, thus decreasing a flow rate of the working fluid and excessively reducing a torque capacity coefficient. This leads to the problem of undesirably lowered potential of the torque converter.
Accordingly, it is an object of the invention to provide a torque converter, capable of suppressing both an increase in curvature loss (energy loss due to curvature) of working fluid at an outflow section of a pump impeller and at an inflow section of a turbine runner and a reduction in torque capacity coefficient with the torque converter flattened.
In order to accomplish the aforementioned and other objects of the present invention, a torque converter comprises a converter cover to which a driving power is transmitted from a driving power source, a pump impeller formed integral with the converter cover, a turbine runner to which the driving power is transmitted through a working fluid from the pump impeller, the turbine runner having a turbine shell, a turbine core, and turbine blades disposed between the turbine shell and the core, a stator disposed between the pump impeller and the turbine runner, a flattening ratio L/D of a sum L of an axial length of the pump impeller and an axial length of the turbine runner to a torque-converter nominal diameter D of the torque converter being set to a value less than or equal to 0.21, and a ratio r/R of a radius of curvature r of a turbine-core outer peripheral curved surface of the core at a turbine inflow section to a radius of curvature R of a turbine-shell outer peripheral curved surface at the turbine inflow section being set to satisfy a predetermined inequality 0.3xe2x89xa6r/Rxe2x89xa60.5.
According to another aspect of the invention, a torque converter comprises a converter cover to which a driving power is transmitted from a driving power source, a pump impeller formed integral with the converter cover, a turbine runner to which the driving power is transmitted through a working fluid from the pump impeller, the turbine runner having a turbine shell, a turbine core, and turbine blades disposed between the turbine shell and the core, a stator disposed between the pump impeller and the turbine runner, a flattening ratio L/D of a sum L of an axial length of the pump impeller and an axial length of the turbine runner to a torque-converter nominal diameter D of the torque converter being set to a value less than or equal to 0.21, and a ratio r/R of a radius of curvature r of a turbine-core outer peripheral curved surface of the core at a turbine inflow section to a radius of curvature R of a turbine-shell outer peripheral curved surface at the turbine inflow section being set to satisfy a predetermined condition that a torque converter efficiency obtained at the radius-of-curvature ratio r/R at which a torque capacity coefficient becomes a maximum torque capacity coefficient is set as a permissible lowest converter efficiency. The predetermined condition may be represented by an inequality Axe2x89xa6r/Rxe2x89xa6B, where A is a lower limit of the radius-of-curvature ratio r/R, obtained when the converter efficiency reduces to the permissible lowest converter efficiency in accordance with a decrease in the radius-of-curvature ratio r/R from a peak point corresponding to a maximum converter efficiency, and B is an upper limit of the radius-of-curvature ratio r/R, obtained when the converter efficiency reduces to the permissible lowest converter efficiency in accordance with an increase in the radius-of-curvature ratio r/R from the peak point corresponding to the maximum converter efficiency. Preferably, the lower limit A is set to 0.3 and the upper limit B is set to 0.5, and the predetermined condition is represented by the inequality 0.3xe2x89xa6r/Rxe2x89xa60.5.
According to a further aspect of the invention, a torque converter comprises a converter cover to which a driving power is transmitted from a driving power source, a pump impeller formed integral with the converter cover, a turbine runner to which the driving power is transmitted through a working fluid from the pump impeller, the turbine runner having a turbine shell, a turbine core, and turbine blades disposed between the turbine shell and the core, a stator disposed between the pump impeller and the turbine runner, a flattening ratio L/D of a sum L of an axial length of the pump impeller and an axial length of the turbine runner to a torque-converter nominal diameter D of the torque converter being set to a value less than or equal to 0.21, and a ratio r/R of a radius of curvature r of a turbine-core outer peripheral curved surface of the core at a turbine inflow section to a radius of curvature R of a turbine-shell outer peripheral curved surface at the turbine inflow section being set to satisfy a predetermined inequality 0.33xe2x89xa6r/Rxe2x89xa60.43.
According to a still further aspect of the invention, a torque converter comprises a converter cover to which a driving power is transmitted from a driving power source, a pump impeller formed integral with the converter cover, a turbine runner to which the driving power is transmitted through a working fluid from the pump impeller, the turbine runner having a turbine shell, a turbine core, and turbine blades disposed between the turbine shell and the core, a stator disposed between the pump impeller and the turbine runner, a flattening ratio L/D of a sum L of an axial length of the pump impeller and an axial length of the turbine runner to a torque-converter nominal diameter D of the torque converter being set to a value less than or equal to 0.21, and a ratio r/R of a radius of curvature r of a turbine-core outer peripheral curved surface of the core at a turbine inflow section to a radius of curvature R of a turbine-shell outer peripheral curved surface at the turbine inflow section being set to satisfy a predetermined condition that a decrease rate of a torque converter efficiency with respect to a maximum converter efficiency is less than or equal to 1%. The predetermined condition may be represented by an inequality Cxe2x89xa6r/Rxe2x89xa6D, where C is a lower limit of the radius-of-curvature ratio r/R, obtained when a rate of change in the converter efficiency reduces to 1% in accordance with a decrease in the radius-of-curvature ratio r/R from a peak point corresponding to a maximum converter efficiency, and B is an upper limit of the radius-of-curvature ratio r/R, obtained when the rate of change in the converter efficiency reduces to 1% in accordance with an increase in the radius-of-curvature ratio r/R from the peak point corresponding to the maximum converter efficiency. More preferably, the lower limit C is set to 0.33 and the upper limit D is set to 0.43, and the predetermined condition is represented by the inequality 0.33xe2x89xa6r/Rxe2x89xa60.43.
According to a still further aspect of the invention, a torque converter comprises a converter cover to which a driving power is transmitted from a driving power source, a pump impeller formed integral with the converter cover, a turbine runner to which the driving power is transmitted through a working fluid from the pump impeller, the turbine runner having a turbine shell, a turbine core, and turbine blades disposed between the turbine shell and the core, a stator disposed between the pump impeller and the turbine runner, a flattening ratio L/D of a sum L of an axial length of the pump impeller and an axial length of the turbine runner to a torque-converter nominal diameter D of the torque converter being set to a value less than or equal to 0.21, and a ratio r/R of a radius of curvature r of a turbine-core outer peripheral curved surface of the core at a turbine inflow section to a radius of curvature R of a turbine-shell outer peripheral curved surface at the turbine inflow section being set to satisfy a predetermined inequality Exe2x89xa6r/Rxe2x89xa6F, where E is a lower limit of the radius-of-curvature ratio r/R corresponding to a maximum converter efficiency and F is an upper limit of the radius-of-curvature ratio r/R corresponding to a maximum torque capacity coefficient. Preferably, the lower limit E is set to 0.37 and the upper limit F is set to 0.5, and thus the ratio r/R is set to satisfy the predetermined inequality 0.37xe2x89xa6r/Rxe2x89xa60.5. The torque capacity coefficient may be represented by an equation xcfx84=Ti/Ni2, where Ti is a magnitude of torque-converter input torque, and Ni2 is a square of torque-converter input rotational speed.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.